Dead Reckoning pedometer

ABSTRACT

A system to determine the location of a person within a structure utilizes a magnetometer, magnets, pressure sensors and a CPU to calculate the length and direction of each step. The data may be displayed to the wearer, preferably on a map or floorplan and may be broadcast to persons outside the structure.

[0001] This invention was made with government support under contractDE-AC09-96SR18500 awarded by the U.S. Department of Energy toWestinghouse Savannah River Company and the government has certainrights in this invention.

BACKGROUND

[0002] 1. Field of the Invention

[0003] This invention relates generally to the determination of thelocation of an individual based upon data collected from magnetometersplaced in the podiatric region and more particularly to determining thelocation of a person or robot in a space lacking benchmarks.

[0004] 2. Background and Prior Art

[0005] The determination of a person's exact location has been achallenge throughout history.

[0006] Landmarks in the form of the rivers and mountains sufficed forprimitive societies. Highway markers resolved the task for latertravelers. Celestial navigation based on the sextant and accuratechronometers made possible marine navigation. All of these methods relyupon fixed points of reference and the person defines his location byreference to the location of the fixed reference point.

[0007] A more difficult problem is posed when the only fixed referencepoint is the point of departure. The problem is raised when a person ora robot must enter a closed location without interior reference pointsor when the person or robot cannot communicate the relationship toreference points to persons outside the location.

[0008] Examples of this condition are rescue persons entering a burningbuilding or robots entering a damaged nuclear reactor.

[0009] Pedometers based upon counting the number of steps taken are wellknown but cannot define direction and must be calibrated for a person'sstride. Electronic pedometers such as that disclosed in U.S. Pat. No.5,724,265 to Hutchings use accelerometers and rotational sensorstogether with a small computer to calculate speed, distance, etc.

[0010] Dead-reckoning devices for vehicles using multiple sensors todetermine speed and heading are disclosed in U.S. Pat. No. 5,075,693 toMcMillan et al. and U.S. Pat. No. 5,764,014 to Jakeway et al. Thesedevices measure distance from wheel rotation, ground track sensors andobtain direction using a magnetometer. Problems with systemic andnon-systemic errors in such systems are described in University ofMichigan Technical Report UM-MEAM-94-22 by Borenstein and Feng.

[0011] A dead-reckoning system for pedestrians is disclosed in U.S. Pat.No. 5,583,776 to Levi et al. and uses an accelerometer to measurefootsteps. The device is calibrated for the user and the resultsroutinely corrected using data from a GPS receiver. Indoor use wouldpreclude use of GPS and be subject to the same (or worse) errors asdescribed by Bornstein et al.

[0012] Magnetometers are instruments used to measure magnetic fields.Particularly useful for navigation are flux-gate or flux-valvemagnetometers which find use in compasses and avionics. Using themagnetic poles of the earth, a three-axis magnetometer can detectdirection, pitch and yaw in an aircraft. The development ofmicroelectronic processing elements renders information frommagnetometers immediately useful and more accurate.

BRIEF SUMMARY OF THE INVENTION

[0013] It is a first object of this invention to provide a means formeasuring the movement of a person in a space lacking good referencepoints. It is a second object of this invention to provide a means foradvising a person of his location relative to a starting point. It is athird object of this invention to provide a record of a person'smovement. It is a fourth object of this invention to provide a means forothers to monitor the position of a person within an enclosure whenvisible reference points are limited or non-existent.

[0014] These and other objectives are obtained by attaching smallmagnets to a person's feet and monitoring the movement of these magnetsusing 3-dimensional magnetometers in conjunction with a computerizedmonitoring system. The results may be displayed for the user orcommunicated to persons at a distance. By use of this invention,firefighters in burning buildings can be located and workers in othermaze-like settings may be followed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 illustrates a person wearing the components of thisinvention.

[0016]FIG. 2 is a block diagram showing the basic system components andlogic of a first embodiment of the invention.

[0017]FIG. 3 is a block diagram showing the basic system components andlogic of a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The dead reckoning pedometer according to this invention has twoelements. A sensing package is mounted at or near each foot and consistsof a magnetic point source, a three-dimensional ma gnetic sensor and afoot pressure sensor.

[0019] The processing package, which may be mounted at the waist, in aback or front pack or in an article of clothing such as a turn-out coat,consists of a computer processing unit including to but not limited to asignal conditioning unit, computer, data bases such as a floor plan, adisplay screen and a transmitter.

[0020] As a separate component, a remote unit such as a radio receiver,display, databases and CPU may be used to follow the person from outsidethe facility. For example, one or more floorplans or architecturaldrawings may be stored and the location of the wearer placed on thefloorplan using three-dimensional CAD programs commercially available.

[0021] Additional sensors may be interfaced to the CPU carried by theperson or may be external, fixed sensors within a facility to assistwith location determination. A firefighter, for example, might carry oneor more of a temperature sensor, oxygen sensor, flammable gas sensor oroxygen flow sensor. External sensors may include motion sensors,microphones, thermoanaemometers, etc.

[0022]FIG. 1 illustrates the invention in terms of a fireman. At or neareach foot are placed a magnet 3, 3′ which may be a permanent magnet oran electromagnet. A pressure sensor (pressure switch) 5, 5′ is mountedin such a location so as to register when that foot is brought into orout of contact with the floor. A magnetometer 7, 7′ is mounted on eachextremity to detect movement of the foot-carried magnets. Wires 9, 9′are run from the feet to the signal conditioning unit 11.

[0023] Most rescue personnel wear a type of boot which can be easilyadapted to be the sensing element of the invention. A firefighter'sboots could easily be modified to carry the necessary items and sensingcables easily connected to a belt mounted unit or to the turn-out coatto isolate them from heat and snagging.

[0024] The basic signals for processing as shown in FIG. 2 would be onor off for each foot pressure sensor and x, y, and z readings asinterpreted from changes in the magnetic field strength from themagnetomer.

[0025] Signal conditioning would include one or more of the followingoperations: a) analog to the digital conversion (ADC); b) high speedsignal samples; c) data logger; central processing unit for analysis ofdata; d) mass storage device; and e) transmitter.

[0026] The output from the magnetometer consists of relative magneticfield strength in the x, y and z directions during each step.

[0027] Outputs are three-dimensional analog signals (voltages) which areconverted to digital intensities by ADC in each direction and time unit.

[0028] Each permanent magnet has a known field strength which falls offwith distance from the magnetometer. Since we are encompassed in theearth's magnetic field, we can get the relative components in the x, y,z directions for each step.

[0029] Commercial magnetometers suitable for use in this invention arethe HMC 1000 series from Honeywell. The magnetometers should becalibrated for the magnets used.

[0030] The output of each magnetometer begins when the pressure sensorswitch on the opposite foot is released and stops when the pressuresensor switch of the opposite foot is activated.

[0031] The relative position of each foot is determined by sampling thechanges in magnetic field in the x, y and z direction during the step.At the completion of the step the new (X, Y, Z) position is establishedas a bread crumb trail.

[0032] Beginning at an arbitrary reference point, e.g., a door, theposition of each foot can be related back to the reference point. Thefrequency of each stride is determined by equation (1)

t _(stop) −t _(start)=frequency of stride (1)

[0033] The length of the stride is determined by equation (2)

H _(stop) −H _(start)=length of stride (2)

[0034] wherein H is the average magnetic flux in Webers. The directionis obtained by subtracting the magnetic flux of the earth from thesensed average flux.

[0035] The distance traveled is obtained by equation (3)

D=(X ₁ −X ₀)²+(Y ₁ −Y ₀)²+(Z ₁ −Z ₀)²  (3)

[0036] where X, Y and Z are the distances from the starting point ineach direction.

[0037] In a second embodiment, as shown in FIG. 3, the movement can beoverlayed onto a digitized map such as a blueprint on three-dimensionaldrawing (CAD) to show the wearer his position. This is best done bydisplay. A simple liquid crystal screen may suffice. For smokylocations, an heads-up display onto a visor may be preferred. Knownreference points within the field also could be displayed.

[0038] The information collected by the wearer also may be transmittedremotely using conventional radio frequency signals. Persons outside theconfined space could follow the progress of the wearer and providedirections as appropriate.

[0039] Other aspects, objects and advantages of this invention may beobtained from a study of the drawings, the disclosure and the appendedclaims.

We claim:
 1. A dead reckoning pedometer comprising: a) a foot pressuresensor attached to each front; b) a magnetic point source attached at ornear each foot; c) a magnetometer attached at or near each foot; d) asignal conditioning unit to process signals from each sensor and eachmagnetometer; e) a computer analysis and data storage unit; f) means fordisplaying the results from said computer analysis.
 2. A dead reckoningpedometer according to claim 1 further comprising a database containingfloorplans.
 3. A dead reckoning pedometer according to claim 1 furthercomprising a radio frequency transmitter.
 4. A dead reckoning pedometeraccording to claim 1 wherein said means for displaying said result is aliquid crystal screen.
 5. A dead reckoning pedometer according to claim1 wherein said means for displaying said result is a heads-up display.6. A method for determining the location of a person using a deadreckoning pedometer comprising: a) means for determining when each footis in contact with a supporting surface; b) means for determining theposition of permanent magnets; c) means to calculate the position ofsaid permanent magnets relative to a previous position.
 7. A methodaccording to claim 6 wherein said means for determining when each footis in contact with a supporting surface is a pressure sensor.
 8. Amethod according to claim 6 wherein said means for determining theposition of permanent magnets is a magnetometer.
 9. A method accordingto claim 6 wherein said means for calculating is a signal conditioningunit and a CPU.
 10. A method according to claim 9 further comprisingdisplaying the results from said calculating on a map.